Yin-Jui Lu

Electronic structures and electron-injection mechanisms of cesium-carbonate-incorporated cathode structures for organic light-emitting devices

In this letter, we investigate electronic structures and electron-injection mechanisms of the effective cathode structures for organic light-emitting devices incorporating cesium carbonate (Cs2CO3), either deposited as an individual thin injection layer or doped into the organic electron-transport layers. The electronic structures and the interface chemistry studied by ultraviolet and x-ray photoemission spectroscopy show that the enhanced electron injection is associated with strong n-doping effects and increase of electron concentrations in the electron-transport layer induced by Cs2CO3. Since such a reaction occurs without the presence of metals, cathode structures incorporating Cs2CO3 may be applied to a wide range of electrode materials.

Effective connecting architecture for tandem organic light-emitting devices

An effective connecting structure for tandem organic light-emitting devices is reported. The connecting structure consists of a thin metal layer as the common electrode, a hole-injection layer containing MoO3 on one side of the common electrode, and an electron-injection layer involving Cs2CO3 on the other side. Such a connecting structure permits efficient opposite hole and electron injection into two adjacent emitting units and gives tandem devices superior electrical and optical performances. Furthermore, the present connecting structure involves no sputtering or handling of reactive metals during device fabrication and can be prepared purely by thermal evaporation, thus rendering device processing more feasible.

Efficient White OLEDs Employing Phosphorescent Sensitization

We have investigated white-emitting organic light-emitting devices (WOLEDs) making use of both blue-phosphor-sensitized orange-red fluorescence and the residual blue phosphorescence. By carefully adjusting the concentrations the phosphor and the fluorophore in the emitting layer and choosing the carrier-transport layers in the device structure, WOLEDs containing a single phosphor-sensitized emitting layer (type-I devices) can give colors close to the equal-energy white (0.33, 0.33), CRI up to 75, and efficiencies up to (10%, 23 cd/A, 13.4lm/W). Furthermore, by doping a green phosphor into the poorly emitting electron-transport layer (type-II devices) to recycle excitons formed there, the EL efficiencies can be further enhanced up to (12.1%, 35.3 cd/A, 23.9lm/W). In both types of devices, the phosphor sensitization reduces population of triplet excitons in the emitting region and substantially mitigates the efficiency roll-off with the driving current or brightness that is often observed in all-phosphor OLEDs. At the brightness of 1000 cd/m2, both types of devices retain quantum and cadmium per ampere (cd/A) efficiencies similar to their peak values

Achieving three-peak white organic light-emitting devices using wavelength-selective mirror electrodes

We report an effective approach based on wavelength-selective mirrors for implementing three-peak white-emitting organic light-emitting devices (OLEDs). Such three-peak white OLEDs have electroluminescence spectra matching better with the transmission spectra of typical color filters and thus give much enhanced color gamut for full-color OLED display applications. The wavelength-selective mirror uses the metal/dielectric stack that is compatible with the OLED fabrication.

Highly efficient tandem organic light-emitting devices utilizing the connecting structure based on n-doped electron-transport layer/HATCN/hole-transport layer

In this work, we conducted studies of tandem organic light-emitting devices (OLEDs) based on the connecting structure consisting of n-doped electron-transport layer (n-ETL)/1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HATCN)/hole-transport layer. We investigated effects of different n-ETL materials and different HATCN thicknesses on characteristics of tandem OLEDs. Results show that the tandem OLEDs with n-BPhen and a 20 nm layer of HATCN in the connecting structure exhibited the best performance. With these, highly efficient and bright green phosphorescent two-emitting-unit tandem OLEDs, with drive voltages significantly lower than twice that of the single-unit benchmark device and current efficiencies higher than twice that of the single-unit benchmark device, were demonstrated.

P‐193: White‐Emitting Tandem Organic Light‐Emitting Devices with an Effective Connecting Architecture

We report efficient white-emitting tandem organic light-emitting devices using an effective connecting structure, which consists of a common electrode and hole-injection/electron injection layers on two opposite sides. This connecting structure involves no sputtering or handling of reactive metals during device fabrication and can be prepared purely by thermal evaporation, thus simplifying device processing.

25.2: Achieving Three‐Peak White Organic Light‐Emitting Devices Using Wavelength‐Selective Mirror Electrodes

We have developed an effective approach based on wavelength-selective mirrors to implement three-peak WOLEDs that have EL spectra matching better with transmission spectra of typical color filters and thus give much enhanced color gamut for full-color OLED display applications. The wavelength-selective mirror used is highly compatible with OLED fabrication.

Electromagnetic Modeling of OLEDs and its Applications to High-cd/A OLEDs

In this paper, general discussions of the optical structures and rigorous electromagnetic modeling of OLEDs are given, and their applications in analyses and designs of various advanced OLED structures like microcavity OLEDs, tandem OLEDs, top-emitting OLEDs and techniques to enhance cd/A efficiencies have been discussed

P‐154: Efficient White OLEDs Employing Phosphorescent Sensitization

Efficient white OLEDs employing phosphorescent sensitization are investigated. Devices with a single phosphor-sensitized emitting layer can give colors close to (0.33, 0.33) and efficiencies up to (10%, 23 cd/A, 13.4 lm/W). Devices with a sensitized emitting layer and a low-concentration phosphorescent layer further enhance the efficiencies up to (12.1%, 35.3 cd/A, 23.9 lm/W). In all phosphor-sensitized WOLEDs, the efficiency roll-off at higher currents is much reduced.

Employing microcavity effects to enhance performances of white-emitting OLEDs

We have developed an effective approach based on wavelength-selective mirrors to implement three-peak WOLEDs that have EL spectra matching better with transmission spectra of typical color filters and thus give much enhanced color gamut for full-color OLED display applications. The wavelength-selective mirror used here is highly compatible with OLED fabrication.